What is the optimal catheter flow rate for dialysis catheters and what are its indications and contraindications?

Catheter Flow for Dialysis Catheters: Indications and Contraindications

The optimal catheter flow rate for dialysis catheters is defined as a blood flow of at least 300 mL/min at a prepump arterial pressure more negative than -250 mm Hg, with catheter dysfunction occurring when this minimum flow cannot be maintained. 1

Definition of Catheter Flow (Cath-Flow)

Cath-flow refers to the blood flow rate through dialysis catheters during hemodialysis treatment. It is a critical parameter that determines the effectiveness of the dialysis procedure and is measured in milliliters per minute (mL/min).

Key parameters for assessing catheter flow:

• Blood pump flow rates (target: ≥300 mL/min)
• Arterial pressure (should not be more negative than -250 mm Hg)
• Venous pressure (should not exceed 250 mm Hg)
• Conductance (ratio of blood flow to absolute value of prepump pressure, should be ≥1.2)
• URR (should be ≥65% or Kt/V ≥1.2)

Indications for Monitoring Catheter Flow

1. Routine dialysis adequacy assessment:

   • Regular monitoring of catheter flow is essential to ensure adequate dialysis delivery
   • Flow rates should be assessed at each dialysis session

2. Early detection of catheter dysfunction:

   • Decreased flow rates may indicate developing problems
   • A dysfunctional catheter is easier to salvage than a nonfunctional one 1
   • Early intervention prevents inadequate dialysis and complications

3. Catheter placement verification:

   • Immediately after catheter insertion to confirm proper positioning
   • Poor flow may indicate improper placement requiring repositioning

4. Post-intervention assessment:

   • After thrombolytic therapy or catheter exchange
   • To verify restoration of adequate flow

Contraindications to High Flow Rates

1. Pediatric or smaller adult catheters:

   • These catheters are not designed for flows exceeding 300 mL/min 1
   • Attempting higher flows may damage the catheter or cause hemolysis

2. Catheter tip malposition:

   • Catheters not positioned at the caval-atrial junction may not support high flows
   • Requires repositioning before attempting high flow rates

3. Mechanical obstruction:

   • Intraluminal thrombus
   • Catheter tip obstruction
   • Fibrin sheath formation
   • Fibrin tail development

4. Catheter integrity issues:

   • Damaged or kinked catheters
   • Risk of catheter rupture with high pressure

Clinical Significance and Management

Importance of Adequate Flow:

• High-efficiency dialysis in the US requires blood flow rates ≥300 mL/min to achieve target single-pool Kt/V of 1.2 1
• Lower flow rates extend treatment times and may result in underdialysis
• Catheter dysfunction leads to 17-33% of untimely catheter removals 1

Management Algorithm for Low Flow:

1. Assess catheter age and position:

   • For recently placed catheters, check for mechanical issues or improper positioning
   • For older catheters (>2 weeks), suspect progressive occlusion

2. Attempt simple interventions:

   • Patient repositioning
   • Catheter flushing
   • Reversal of lines (temporary measure, increases recirculation)

3. If flow remains inadequate, consider:

   • Thrombolytic therapy using intraluminal lytic agents
   • Intradialytic lock protocol
   • Intracatheter thrombolytic infusion or interdialytic lock 1

4. For persistent dysfunction:

   • Catheter exchange over guidewire if no infection is present
   • Replacement with new catheter if necessary

Important Considerations and Pitfalls

Recirculation Issues:

• Recirculation significantly increases with femoral catheters (13.1%) compared to internal jugular catheters (0.4%) 1
• Shorter femoral catheters (<20 cm) have higher recirculation (26.3%) than longer ones (8.3%) 1
• Line reversal increases recirculation from 2-3% to >10%, reducing dialysis efficiency 1

Common Pitfalls:

• Overreliance on a single flow threshold: Research shows that mean blood flows <300 mL/min are not always associated with dialysis inadequacy 2
• Ignoring prepump arterial pressure: Flow must be assessed in conjunction with pressure readings
• Delayed intervention: Waiting until flow decreases to 300 mL/min may be too late to prevent catheter loss 1
• Neglecting trend analysis: Progressive decline in flow is more significant than a single low reading

Flow Optimization:

• The optimal ratio of blood flow rate (QB) to dialysis fluid flow rate (QD) should be maintained at 1:2 3
• For catheters with lower flow capabilities, consider extending treatment time to achieve adequate dialysis

By maintaining optimal catheter flow and promptly addressing dysfunction, patient morbidity and mortality can be reduced while ensuring adequate dialysis delivery.